1. Field of the Invention
The present invention relates to organic light emitting diodes including organic layers comprising organic metal complexes. More particularly, the invention is directed to organic light emitting diodes including organic layers comprising oligomer type organic metal complexes.
2. Description of the Related Art
Organic light emitting diodes (OLEDs) are self-emissive light-emitting devices. OLEDs have wide viewing angles, good contrast and quick response time, and implement full color images.
In a conventional organic light emitting diode, an anode is formed on a substrate. A hole transport layer, an emissive layer, an electron transport layer and a cathode are sequentially formed on the anode. When a current is applied to the anode and the cathode, electrons injected from the cathode migrate to the emissive layer via the electron transport layer. The electrons are recombined in the emissive layer with holes injected from the anode to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted from the emissive layer, thereby forming an image. An exciton can be in one of two states: singlet or triplet. The light that is emitted when excitons drop to the ground state from a singlet excitation state is referred to as “fluorescence.” The light that is emitted when excitons drop to the ground state from a triplet excitation state is referred to as “phosphorescence.” Fluorescence having a 25% probability of a singlet excitation state (triplet excitation state: 75%) has low luminous efficiency, whereas phosphorescence having a 25% probability of a singlet excitation state and a 75% probability of a triplet excitation state can theoretically have an internal quantum efficiency of about 100%. However, in conventional organic light emitting diodes, it is difficult to obtain satisfactory electrical properties.